Process for the continuous casting of tubular products



Oct-Q10, 1967 B- TARMANN 3,345,036

PROCESS FOR rm; Co'mmuous CASTING OF TUBULAR PRODUCTS Fil ed Jan. 8, 1965 FIG],

United States Patent ()fiice 3,346,036 Patented Oct. 10, 1967 PROCESS FOR THE CONTINUOUS CASTING OF TUBULAR PRODUCTS Bruno Tarmann, Kapfenberg, Austria, assignor to Gebr. Bohler & Co., Alttiengesellschaft, Vienna, Austria Filed Jan 8, 1965, Ser. No. 424,297

Claims priority, application Austria, Jan. 16, 1964,

17 Claims. (Cl. 164--85) Since the time when a continuous casting of highamelting alloys, particularly of iron and steel, was feasible, there have been numerous suggestions and attempts to also make tubular castings in this manner. Usually, the liquid metal was poured into the annular space between a water-cooled mold for continuous casting and a watercooled core, and the tubular casting was continuously lower from the mold, possibly in a partially solidified state. Owing to the numerous relations between the factors to be considered, such as pouring rate, pouring temperature, taper of the mold and of the core, cooling effect of the mold and core, properties of various alloys, this casting process can be performed only with great difficulty so that it has not found widespread application.

It is an object of the invention to eliminate the disadvantages of the known processes and provide a process which can be carried out on a commercial scale. To accomplish these objects, the invention provides a process for the continuous casting of tubular products, particularly tube blanks, in which, just as in the casting of solid products, molten material is poured in known manner in the top end of an open-ended mold for continuous casting and the partially solidified casting withdrawn from such mold is guided along an initially descending and then an ascending, curved path to a level in which the liquid part of the casting cannot rise further so that the liquid metal inside the casting rises only to that level as pouring and withdrawing of the casting is continued, whereas the casting drawn beyond said level is hollow.

Because the process according to the invention does not use a water-cooled mold core for shaping the cavity of the casting, all disadvantages previously caused by such water-cooled core are eliminated. In addition, all means for holding, moving and cooling the mold core are eliminated so that the casting equipment is greatly simplified. Known means, which have proved satisfactory for casting solid products and are reliable in operation, may be used for charging and distributing the metal. The conveyance and cooling of the casting when it has left the mold may also be carried out as in the case of solid castings. The casting, however, is not guided along a curved path only to the level of the mold outlet and then straightened, as is known, but its movement along a curved path is continued, e..g., to the level of liquid metal in the mold. On

' this level, the pressure in the liquid core of the casting is just as high as the pressure of the atmosphere surrounding the casting if the surface of the liquid metal in the mold is also subjected to atmospheric pressure. If an opening is provided in the solidified skin of the casting on this level, e.g., by means of a cutting torch, or the starting end or plug is entirely severed, the curved casting 'will form an approximately U-shaped vessel having communicating limbs. In the interior of the casting, the melt extends from the surface of the molten metal in the mold to the point where the casting has again reached the level of this surface. That portion of the casting which rises above this liquid level is hollow and may be bent into a horizontal direction or may be cut into the desired lengths while moving further along an ascending path.

On the other hand, if the surface of the molten metal in the mold is not subjected to the normal atmospheric pressure but to a higher or lower pressure, the lowest level on which the casting can be cut open without risk of an outflow of liquid metal will be shifted downwardly or upwardly, depending on the pressure conditions.

According to the invention, hollow bodies may also be made without opening the skin of the casting. In this case, the casting must be moved along the ascending 'path at least to that level in which a vacuum will be formed inside the casting. This level will depend on the pressure conditions and is about 1.40 meters above the surface of the molten metal in the mold if this surface is subjected to normal atmospheric pressure. An increasing vacuum on this surface will lower the liquid level inside the casting toward that of the surface of the molten metal in the mold.

Compared to the continuous casting of tubular prodnets with the aid of a cooled mold core, the tubular products made according to the invention have a perfectly tight wall. This advantage can easily be understood because it is known that porous portions or voids formed during the solidification of wells are mainly formed where solidification fronts meet. In the process according to the invention, however, there is only one solidification front, which is shifted from the exterior surface of the casting in an inward direction and from the upper end of the melt in the ascending limb and forms the inside surface of the hollow casting. In casting tests, it has been found that the inside surface of the tubular casting formed in this manner is surprisingly smooth so that the tubular castings obtained by the invention are highly suitable for being processed into seamless tubes.

The process according to the invention is preferably carried out the aid of an arcuate mold, which is left by the casting in a curved form so that the initially thin and sensitive skin of the casting is not subjected to bending stress. In this case that are of the casting which is 'below the surface of the molten metal in the mold may be particularly short so that tubular castings having a small wall thickness may be made.

For instance, a tubular casting may be made according to the invention as follows: Liquid steel is charged into a water-cooled mold for continuous casting in known manner from a conventional ladle with the aid of an offset tundish. The mold cavity has a circular cross-section and is curved according to an arc of a circle, the axis of the mold cavity forming a part of a circle. Only a part of the casting is solidified in the mold so that the casting which emerges from the mold and is shaped according to an arc of a circle has a liquid core. In close succession to the mold, the casting is moved along a path which is also arcuate or circular to the level of the top of the mold by means of guide rollers, at least some of which are driven. During this movement, the casting is cooled further by sprayed cooling water so that its solidified skin increases in thickness. As soon as the starting end of the casting has reached said level, the cold starter bar or plug is severed and an opening is formed in the skin of the casting by a torch approximately on the level where the liquid core of the casting begins. The casting emerging upwardly from the guide path is straightened by a multiroller straightener and is then cut with cutting torches to the desired length. When the casting process is terminated, the withdrawal of the casting must be interrupted until the casting has completely solidified because liquid steel would otherwise flow about the equipment. Hence, the last portion of the casting is not hollow. A tubular casting made in this manner from steel containing, e.g., 1% carbon and 1.5% chromium has an outside diameter of about 150 mm. and an inside diameter of about 50 mm. when the mold cavity is 150 mm. in diameter, the radius of the curved axis of the mold cavity and of the curved guide means for the casting is 1.5 meters, and the pouring and withdrawing speed is 1.5 meters per minute, cooling water being used at the same rate as with solidcastings.

To make tubular castings having a larger wall thickness, molds having a straight axis may be used and the casting may be guided along a curve (for instance of circular, parabolic or clothoid-shape) only from a point spaced below the mold with the aid of guide rollers. In any case, the liquid core in the casting must have a liquid top surface exposed to the interior of the tubular casting.

According to the invention, the wall thickness of the tubular casting to be made is controlled by a suitable design of the curved path for the casting below the level of the melt in the mold and by a control of the pouring speed and/ or of the direct water cooling. In making tubular castings having a particularly small wall th ckness, it may even be necessary to cool only a short portion of the casting emerging from the mold with sprayed water and to provide a suitable heat insulation for the ca-stingm the remainder of the curved path traversed by the casting having a liquid core, in order to inhibit a further dissipation of heat.

The uniformity of the wall thickness and the quallty of the inside surface of the tubular castings made according to the invention may be improved by the action of electromagnetic fields or of vibrators on the liquid core of the casting so as to agitate this liquid core and ensure an equalization of temperature.

The process according to the invention may be applied to special advantage to circular or square cross-sections.

The invention provides also improved apparatus for the continuous casting of tubular products. Two embodiments of the invention are shown by way of example in FIGS. 1 and 2, respectively, of the drawings in diagrammatic vertical sectional views, in which like reference numerals refer to analogous parts.

In both embodiments, molten steel is discharged from a ladle 1 into an offset tundish 2, from which the melt is poured into the top end of a water-cooled mold for continuous casting. This mold extends generally vertical and has open top and bottom ends. The casting emerging from the bottom end of the mold has a solidified skin and a liquid core. This casting is positively fed and guided along an arcuate path having a descending initial portion and an ascending succeeding portion by guiding rollers 4, which engage opposite sides of the casting. At least part of said guiding rollers 4 are driven feeding rollers, which serve to advance the casting along the curved path.

The ascending portion of the curved path defined by the guiding rollers 4 extends above the level of the top surface 7 of the liquid core of the castings 5 in the ascending portion of the curved path. Above this level, a torch symbolized by an arrow 6 may be applied to form an opening through the skin of the casting 5. Through this opening, the interior of the hollow casting above the liquid-gas interface 7 at the top of the liquid core communicates with the outside atmosphere and maintain barometric equilibrium. This top surface of the liquid core is on the same level as the top surface of the molten material in the mold 3.

The guiding rollers 4 are arranged to feed the casting 5 as a hollow casting beyond the interface 7.

The two embodiments differ in that in FIG. 1 the axis of the mold 3 is curved according to an arc of a circle and the guiding rollers 4 are arranged so that the axis of the casting 5 guided by said rollers along the curved path follows an arc of the same circle as the axis of the mold.

In FIG. 2, the axis of the mold 3 is straight and the guiding rollers 4 are arranged to deflect the casting 5 gradually from the direction of the axis of the mold 3 into the curved path.

What is claimed is:

1. A process for the continuous casting of hollow metal products, which comprises pouring molten metal into the top end of a generally downwardly extending open-ended mold of a desired internal configuration to continuously form the outer surface of the metal as it is poured into a casting in conformity with the internal configuration of the mold, withdrawing such casting having a solidified skin and a liquid core from the other end of the mold, moving said withdrawn casting from the mold in an arcuate path along an initially descending and a subsequently ascending, curved path extending upwardly to a level barometrically equivalent to the level of the molten metal in the mold, and establishing a barometric equilibrium between the surface of the molten metal in the mold and the molten metal in the core in the ascending path to provide a liquid-gas interface at the top of said liquid core in said casting in the ascending portion of said path, the casting fed beyond said interface being hollow.

2. A process as set forth in claim 1, in which said casting is a tube blank.

3. A process as set forth in claim 1, in which a communication is established between the interior of the hollow casting above said interface and the outside atmosphere.

4. A process as set forth in claim 1, in which said barometric equilibrium is established by cutting an opening through the skin of said hollow casting.

5. A process as set forth in claim 1, in which the barometric equilibrium is established by severing the starting end of said casting above said interfere.

6. A process as set forth in claim 1, in which the rate at which molten metal is poured into the top end of said mold is controlled to determine the wall thickness of said hollow casting.

7. A process as set forth in claim 1, in which said casting is cooled at a controlled rate while being guided along said curved path to determine the wall thickness of said hollow casting.

8. A process as set forth in claim 1, which comprises subjecting said liquid core to the action of mechanical means to agitate said liquid core.

9. A process as set forth in claim 1, which comprises subjecting said liquid core to the action of vibrators to agitate said liquid core.

10. A process as set forth in claim 1, which comprises subjecting said liquid core to the action of electrically operated means to agitate said liquid core.

11. A process as set forth in claim 1, which comprises subjecting said liquid core to the action of electromagnetic fields to agitate said liquid core.

12. A process as set forth in claim 1, in which the interior of said hollow casting is maintained sealed from the ambient atmosphere and the surface of the molten metal in said mold is maintained under a sufficiently low pressure so that a vacuum is maintained in said ascending portion above said interface.

13. A process as set forth in claim 12, in which said ascending portion of said path extends above the surface of said molten metal in said mold.

14. A process as set forth in claim 12, in which the surface of said molten metal in said mold is subjected to a subatmospheric pressure.

15. A process as set forth in claim 1, which comprises cooling said casting in an initial portion of said path and retarding the dissipation of heat from said casting in a succeeding portion of said path below said interface.

16. A process as set forth in claim 1, in which said molten metal is poured into the top end of a mold extending along an arc of a circle and said curved path extends along an arc of a circle to a point above the level of the surface of molten metal in said mold.

17. The process as claimed in claim 1 in which the molten metal is poured and the casting is Withdrawn at the same linear distance per minute as the radius of curvature of said arcuate path.

References Cited UNITED STATES PATENTS Phillips et a1. 2257.2 Rossi 22-57.2

Korb 2257.2 Schneckenborger et a1. 22-57.2

6 3,045,299 7/ 1962 Steigerwald 2257.2 3,153,820 10/1964 Criner 22216 X 3,157,920 11/1964 Hess 22-572 FOREIGN PATENTS 123,117 12/1946 Australia. 1,327,931 4/ 1963 France.

I. SPENCER OVERHOLSER, Primary Examiner. 10 R. S. ANNEAR, Assistant Examiner. 

1. A PROCESS FOR THE CONTINUOUS CASTING OF HOLLOW METAL PRODUCTS, WHICH COMPRISES POURING MOLTEN METAL INTO THE TOP END OF A GENERALLY DOWNWARDLY EXTENDING OPEN-ENDED MOLD OF A DESIRED INTERNAL CONFIGURATION TO CONTINUOUSLY FORM THE OUTER SURFACE OF THE METAL AS IT IS POURED INTO A CASTING IN CONFORMITY WITH THE INTERNAL CONFIGURATION OF THE MOLD, WITHDRAWING SUCH CASTING HAVING A SOLIDIFIED SKIN AND A LIQUID CORE FROM THE OTHER END OF THE MOLD, MOVING SAID WITHDRAWN CASTING FROM THE MOLD IN AN ARCUATE PATH ALONG AN INITIALLY DESCENDING AND A SUBSEQUENTLY ASCENDING, CURVED PATH EXTENDING UPWARDLY TO A LEVEL BAROMETRICALLY EQUIVALENT TO THE LEVEL OF THE MOLTEN METAL IN THE MOLD, AND ESTABLISHING A BAROMETRIC EQUILIBRIUM BETWEEN THE SURFACE OF THE MOLTEN METAL IN THE MOLD AND THE MOLTEN METAL IN THE CORE IN THE ASCENDING PATH TO PROVIDE A LIQUID-GAS INTERFACE AT THE TOP OF SAID LIQUID CORE IN SAID CASTING IN THE ASCENDING PORTION OF SAID PATH, THE CASTING FED BEYOND SAID INTERFACE BEING HOLLOW. 